888 research outputs found
The 18S ribosomal RNA sequence of the sea anemone <i>Ammonia sulcata</i> and its evolutionary position among other eukaryotes
Evolutionary trees based on partial small ribosomal subunit RNA sequences of 22 metazoa species have been published [(1988) Science 239, 748-753]. In these trees, cnidarians (Radiata) seemed to have evolved independently from the Bilateria, which is in contradiction with the general evolutionary view. In order to further investigate this problem, the complete srRNA sequence of the sea anemone Ammonia sulcata was determined and evolutionary trees were constructed using a matrix optimization method. In the tree thus obtained the sea anemone and Bilateria together form a monophyletic cluster, with the sea anemone forming the first line of descent of the metazoan group
Equivalence of Kinetic Theories of Bose-Einstein Condensation
We discuss the equivalence of two non-equilibrium kinetic theories that
describe the evolution of a dilute, Bose-Einstein condensed atomic gas in a
harmonic trap. The second-order kinetic equations of Walser et al. [PRA 63,
013607 (2001)] reduce to the Gross-Pitaevskii equation and the quantum
Boltzmann equation in the low and high temperature limits, respectively. These
kinetic equations can thus describe the system in equilibrium (finite
temperature) as well as in non-equilibrium (real time). We have found this
theory to be equivalent to the non-equilibrium Green's function approach
originally proposed by Kadanoff and Baym and more recently applied to
inhomogeneous trapped systems by M. Imamovi\'c-Tomasovi\'c and A. Griffin
[arXiv:cond-mat/9911402].Comment: REVTeX3, 6 pages, 2 eps figures, published version, minor change
Oximetry and Glucose Sensors A SMART SENSOR FOR BIOMEDICAL APPLICATIONS
Abstract Monolithic smart sensors for the voltammetric measurement of glucose or oxygen concentrations have been developed. Each smart sensor consists of a planar voltammetric sensor, a CMOS interface circuit and temperature sensor. The interface circuit and the temperature sensor are realised in a standard CMOS process. The sensor specific layers are added afterwards on the same chip with the CMOS compatible sensor technology developed for this purpose. Two versions of this smart sensor have been realised. The two electrode configuration with a Au working electrode has been implemented for the measurement of p02. The three electrode configuration with a Pt working electrode can measure glucose when an additional glucose oxidase membrane is applied on the electrodes. The interface circuit can apply voltages from +lV to -lV to the sensor and can handle sensor current ranges from 30 nA full scale to 1 pA full scale with a +/-2.5 V supply voltage. The temperature sensor has a sensitivity of 154 pV/K. The total dimensions of this smart sensor are 0.75 mm by 5 mm
White Dwarf - Red Dwarf Systems Resolved with the Hubble Space Telescope: I. First Results
First results are presented for a Hubble Space Telescope Advanced Camera for
Surveys snapshot study of white dwarfs with likely red dwarf companions. Of 48
targets observed and analyzed so far, 27 are totally or partially resolved into
two or more components, while an additional 15 systems are almost certainly
unresolved binaries. These results provide the first direct empirical evidence
for a bimodal distribution of orbital separations among binary systems
containing at least one white dwarf.Comment: 46 pages, 3 figures, 5 tables, accepted to ApJ. Full-resolution
images available upon request. A few table entries correcte
Magnetic susceptibility of EuTe/PbTe Heisenberg superlattices: experimental and theoretical studies
We report results on the temperature dependence of the susceptibilities of a
set of MBE-grown short-period EuTe/PbTe antiferromagnetic superlattices having
different EuTe layer thicknesses. In-plane and orthogonal susceptibilities have
been measured and display a strong anisotropy at low temperature, confirming
the occurrence of a magnetic phase transition in the thicker samples, as seen
also in neutron diffraction studies. We suggest that dipolar interactions
stabilize antiferromagnetic long-range order in an otherwise isotropic system
and we present numerical and analytical results for the low-temperature
orthogonal susceptibility.Comment: 30 pages, 8 ps figures, RevTe
Near-infrared spectro-interferometry of three OH/IR Stars with the VLTI/AMBER instrument
We investigate the molecular and dusty environment of OH/IR stars in order to
characterize the mass-loss process during the tip-AGB superwind phase.
Employing the AMBER instrument at the VLT Interferometer we obtained
near-infrared H- and K-band spectro-interferometric observations of the three
OH/IR stars IRAS 13479-5436, IRAS 14086-6907 and IRAS 17020-5254 with a
spectral resolution of about 35. We use a two-component geometrical model,
consisting of a uniform disk and a Gaussian disk, to obtain characteristic
angular sizes of the central stellar sources and their dust envelopes, as well
as the flux ratios between these components. Angular uniform disk diameters of
the three central components of the objects above have values between 3.2 mas
and 5.4 mas. For their dust envelopes, we find FWHM values between 17.1 mas and
25.2 mas. According to distance estimates from the literature, the central
stellar components have radii between 900 R_sun and 1400 R_sun, while their
dust envelopes reach FWHM values between 9000 R_sun and 13000 R_sun. The
visibility functions of all three sources exhibit wavelength variations that
resemble those of earlier VLTI/AMBER observations of semi-regular and Mira
variable AGB stars. These are interpreted as characteristic of atmospheric
molecular layers lying above the photosphere. We also find that the dust
envelopes have a clearly larger optical depth than those known for Mira stars.
We interpret this as an expected result of the "superwind" phase, the final 10
000 to 30 000 years of AGB-evolution, when the mass-loss rate increases by a
factor of 10-100. By their different optical depths, the three dust shells
studied here may represent different stages of the "superwind" and different
initial masses.Comment: 5 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
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